In-vacuum dry launching of silica microparticles using an array of custom MEMS devices

To test the validity of the quantum superposition principle at unprecedented macroscopic scales, near-field matter-wave interferometry of free-falling massive 100nm silica nanospheres from an optically cooled laser trap has been proposed [Nat. Commun. 5, 4788 (2014)]. This could be realized with available technology, providing the emerging technical challenge of in-vacuum dry loading the optical trap with single 100nm silica particles, in a deterministic, repetitive, and clean manner, is addressed. Here, for the first time to our knowledge, we demonstrate, both theoretically and experimentally, a 3×3 array of custom micro-electromechanical system (MEMS) storage and release devices for this objective. The fabricated MEMS devices are square ultrasonic flexural silicon membranes, 400µm in side length and 8µm in thickness, monolithically integrated with a 1µm thick aluminium nitride piezoelectric transducer. The ability of the MEMS array to launch 9.98µm, 4.23µm, and 900nm silica particles in vacuum was tested experimentally using our recently developed GRIN lens-based digital holographic 3D imaging system integrated into a vacuum chamber. The minimum particle size released from the current devices is ∼4µm in diameter with the average lateral release speed in the range of 3-35 cm/s. The experimental results obtained are in good agreement with the theoretical predictions.